1. Field of the Invention
The present invention is related to a wire bonding apparatus and a wire bonding method.
2. Related Art
There exists a wire bonding process, wherein an electrode on a semiconductor chip, and an inner lead formed on a wiring board or a lead frame are electrically connected with a thin metal line (a wire), as part of a semiconductor device manufacturing process.
In the wire bonding process, first, a wire is melted by applying a high voltage electric discharge to the wire (tail) protruding from a tip of a capillary, which forms a ball on the tip of the tail. Then, with the application of heat, pressure, and an ultrasonic oscillation, bonding of this ball and an electrode on a semiconductor chip is performed.
Afterward, this capillary is raised and moved atop an inner lead, and with the application of heat, pressure, or an ultrasonic oscillation, bonding of the wire and the inner lead is performed. When the bonding is complete, the capillary is raised to a prescribed height, and the wire is cut by clamping the wire.
The wire cutting on the inner lead is termed the “tail cut action”, and by tail cutting, a tail of suitable length is left on the tip of the capillary. Wire bonding is performed by carrying out the above described series of actions repeatedly.
In tail cutting, the bond strength of the inner lead and the wire must be just right. For example, in a case in which the bond strength of the inner lead and the wire is too weak, the wire will detach from the inner lead thus making it impossible to perform tail cutting.
On the other hand, in a case in which the bond strength of the inner lead and the wire is too strong, the wire will be severed at the top of the inner lead, and a tail of appropriate length will not be formed. There is a problem in that if there exists no tail of appropriate length, a ball of correct shape would not be formed, whereby if wire bonding is attempted in such a state, the capillary and the electrode on the semiconductor chip would come into direct contact and thereby damage the semiconductor chip and the electrode.
In order to solve this problem, a device is proposed (For example, see Japanese Patent Laid-Open No. 07-106365) that monitors and measures the length of a tail left behind on a capillary tip after tail cutting.
Also, since a great breaking load is incurred on the wire at the time of tail cutting, a spring back phenomenon occurs after the cut, and the wire buckles (deforms). There is a problem in that since this deformed wire is used afterward in wire bonding, this deformed wire would come in contact with adjacent wire connections and create a short defect, thus reducing yield.